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Discussion Starter · #1 ·
I have a 1983 420 with 1500 hours bought it a few months ago. It slows down going up hill. There is no resistance when on flat ground and it mows with great power. Also goes fast in reverse and forward so it’s not slipping. Is this the first sign of the hydro getting old? When it gets to the top of the hill it speeds right up and I have to lower the lever to slow down. I did the full tune up new fluids nothing changed, also adjusted the forward and reverse thinking the forward was not set right that didn’t fix it. Any suggestions or is she tired and I’ll be needing to replace the hydro soon? Thanks, Rob
 

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Slowing on a grade is a sign of worn ground speed control linkage -- there are many threads on this in the forum. Here is a typical one:

Chuck
 

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Discussion Starter · #3 ·
Slowing on a grade is a sign of worn ground speed control linkage -- there are many threads on this in the forum. Here is a typical one:

Chuck
Thanks Chuck I’ll pull the seat pan off and start looking around.
 

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Also note that you may not "see' the small slack movements that worn linkages may have that can cause variation in ground speed. You may have to take the linkages apart to verify that no wear is present...it does not take much slop to cause the symptom to be quite evident.

Chuck
 

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I have the opposite problem with my 420. It speeds up and I have to keep pulling it back. I'm trying to finish the mowing season and then dig into the problem after that. It's not a problem to keep using it as long as I work the hydro lever a bit to maintain a steady speed.

I have a 1983 420 with 1500 hours bought it a few months ago. It slows down going up hill. There is no resistance when on flat ground and it mows with great power. Also goes fast in reverse and forward so it’s not slipping. Is this the first sign of the hydro getting old? When it gets to the top of the hill it speeds right up and I have to lower the lever to slow down. I did the full tune up new fluids nothing changed, also adjusted the forward and reverse thinking the forward was not set right that didn’t fix it. Any suggestions or is she tired and I’ll be needing to replace the hydro soon? Thanks, Rob
This is spot on. There are a bunch of ways the hydro linkage can give trouble and some of them aren't obvious. Gotta do what Chuck said and check all the individual wear points. I don't usually check them though. I just automatically assume I need to replace all the small parts. The hydro linkages on my 400's look like a Rube Goldberg design to me. The steering systems are just as funky. The 420 is better than a 400 but there's still too many ways for problems to occur.

Also note that you may not "see' the small slack movements that worn linkages may have that can cause variation in ground speed. You may have to take the linkages apart to verify that no wear is present...it does not take much slop to cause the symptom to be quite evident.

Chuck
 

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Discussion Starter · #6 ·
I have the opposite problem with my 420. It speeds up and I have to keep pulling it back. I'm trying to finish the mowing season and then dig into the problem after that. It's not a problem to keep using it as long as I work the hydro lever a bit to maintain a steady speed.



This is spot on. There are a bunch of ways the hydro linkage can give trouble and some of them aren't obvious. Gotta do what Chuck said and check all the individual wear points. I don't usually check them though. I just automatically assume I need to replace all the small parts. The hydro linkages on my 400's look like a Rube Goldberg design to me. The steering systems are just as funky. The 420 is better than a 400 but there's still too many ways for problems to occur.
Hi Army so all you have to do is tighten the lock nut securing the brake plate on your linkage so the lever stays in place.
 

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Yup I tried that. A couple times actually. The lever actually works fine till about 4/5 of the way ahead. Problem starts right at the bottom of the little tractor/arrow icon at the top of the forward slot on the dash. It will start gradually moving ahead on its own from that point upward. And of course(!) it starts doing it right where the sweet spot for mowing ground speed is. Probably not a coincidence. It has likely been used in that position a lot. If I pull the lever back a bit from that point so it stays put the mowing speed is too slow. If I tighten the friction adjustment to deal with the sloppiness in the upper range of the lever it's too hard to move it before it gets to that point. A classic Catch 22.
 
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I'm gonna take the hydro control linkage on the 420 apart this winter and replace the worn parts (assuming they're still available) and then do the adjustment. Lots of ways wonky problems can happen. I replaced the control lever on a 400 a few years ago. It was worn bad where it pivots at the bottom. A new one is easy to fab. Just need some rod the right diameter, some heat to do the bends and a tap & die set to cut the threads. I wire wheeled the one I made till it had a nice shiny finish then clear coated it.

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Army,

You may find the plate where the friction disc is providing retaining force has a slick area or taper worn to its surface... What version of the linkage does your tractor have? You map this from the SN of the tractor...

Chuck
 

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This was my rod going back to the transmission on my 1990 420. The holes don't look too wallered out,
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but enough to add quite a bit of movement before the lever, on the side of the transmission, would respond. Had my brother weld the holes, and redrill.
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Discussion Starter · #12 ·
I bet that’s what’s wrong with mine because another issue I have is when I push the lever forward it takes about 2 inches before it starts moving forward. I’ll probably take apart as a winter project. It still works fine just annoying.
 
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